The very fact of Mrs. Gandhi's visit here is a plus for the Soviets and could help to bury the resentment she is said to feel at having been nimbly ''dropped'' by the Kremlin after Indian voters ousted her in 1977.

The Soviets will also appreciate Mrs. Gandhi's public signals here that her vision of nonalignment continues to imply a politely balanced brand of criticism of the Soviet troop presence in Afghanistan. At a news conference Sept. 22, she repeated that she would like the Soviets to leave ''because we are against any type of interference.''

But she added: ''There are two sides to the question. . . . There is interference in Afghanistan's affairs. . . . Insurgents or rebels are being helped with weapons from the outside.''

Overflying Afghanistan en route to the Soviet capital, Mrs. Gandhi dispatched greetings to Afghan leader Babrak Karmal, the kind of testimony to Mr. Karmal's political legitimacy that the Soviets keenly desire from the rest of the region and the world.

During her visit, Mrs. Gandhi has also delivered warm rhetorical tributes to Indo-Soviet friendship.

Yet while diplomats say her visit has gone generally well for the Soviets, it seems to have produced more symbol than substance so far.

Diplomats note that Mrs. Gandhi has sought to avoid lining up publicly with her Soviet hosts in explicit criticism of the United States.

So far, there has been no sign that any new weapons deal has bean signed during the visit. Mrs. Gandhi has recently sought to diversify arms sources and thus dilute India's heavy reliance on Soviet relations.

On India's relations with China, Mrs. Gandhi is said to have been cautioned by Soviet leaders on Peking's alleged ultimate aim to dominate all of Asia. For her part, the Indian leader has reaffirmed her intention to explore improvement of ties with both China and Pakistan, although assuring her hosts that this is not directed against any ''third country.''

She also publicly reaffirmed her ''anxiety at the induction of sophisticated weaponry into our immediate neighborhood,'' a reference to a Reagan administration move to provide Pakistan with new US warplanes and other equipment.

The single most important substantive result so far to emerge from Mrs. Gandhi's visit is a Soviet offer to supply a powerful nuclear reactor to India. The offer follows Indo-American strains over Washington's refusal to supply nuclear fuel for an existing reactor because the Indians have barred inspection of the facility.

During Mrs. Gandhi's visit to Washington, a compromise was reached whereby France might supply the fuel, but the French, too, seem to be insisting on safeguards India will not accept.

But the Soviet Union, too, has traditionally favored strict safeguards on the export of nuclear materials. And Mrs. Gandhi's restrained public comment on the reactor offer, saying the question was being turned over to specialists for further study, suggested to diplomats here that Moscow may also have insisted on controls India will be reluctant to accept.

Foreign diplomats here assume that Mrs. Gandhi's visit will at least help clear the air in Soviet-Indian relations. For Moscow, this would be particularly welcome at a time when the Indian prime minister is expected to be the next chairperson of the nonaligned movement.

After the visit, diplomats suggest, the Soviets are likely to continue conveying concern over India's still embryonic moves toward rapprochement with China and Pakistan, stressing that reinforced Indian-Soviet ties afford Mrs. Gandhi her best protection against traditionally hostile neighbors.

At the same time, the Soviets themselves are repeating their hope for eventually repaired relations with Peking. Diplomats here have little doubt that one of various catalysts for this is India's recent opening of talks with China on their longtime border dispute.

For now at least, the Soviet troop presence in Afghanistan seems a given in the regional policy equation.

Indian sources in effect are echoing the impression of other foreign visitors who recently discussed the Afghan crisis here: that although the Soviets clearly would welcome a political resolution leaving a viable and friendly government in power in Kabul, they are nibbling at none of the specific suggestions so far on the international diplomatic table and seem to be planning no early troop pullout.